JPH02165571A - Solid electrolytic tube for sodium-sulfur battery and its surface shaping - Google Patents

Abstract

PURPOSE:To improve durability by defining an average roughness and the maximum height of the surface of a solid electrolytic tube as a center-line average roughness and the maximum height to set the average roughness and the maximum height of a protorusion portion as specified values. CONSTITUTION:For a solid electrolytic tube 4, a center-line average roughness (Ra) of the surface 4a is set as 2.0mum or less, and the maximum height (Rmax) of the protrusion portion 7 as 15mum or less. In case it is used for a sodium-sulfur battery, fine roughness of the surface prevents centralization of sodium ions or sulfur and even sodium polysulfide which have contact with the surface of the solid electrolytic tube on the local portions of the surface of the solid electrolytic tube. Also, when the sodium-sulfur battery is heated and cooled, the centralization of thermal stress on the solid electrolytic tube surface is relaxed, so that deteriolation of the solid electrolytic tube is restrained. It is thus possible to improve durability of the solid electrolytic tube 4.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a solid electrolyte tube for a sodium-sulfur battery and a method for shaping the surface of the solid electrolyte tube. The present invention relates to a solid electrolyte tube that can be improved and a method for shaping its surface.

(Prior art) Recently, as a secondary battery for electric vehicles and nighttime power storage, it has been developed to be excellent in both performance and economical aspects.
Research and development is progressing on high-temperature sodium-sulfur batteries that operate at ℃.

Conventionally, as shown in FIG. 3, this sodium-sulfur battery includes a cylindrical anode container 1 that houses a conductive material M for the anode, such as a carbon mat impregnated with molten sulfur S, which is an anode active material, and the anode container 1. A cathode container 3 is connected to the upper end of the l through an insulating ring 2 made of α-alumina and stores molten metal Na, and a cathode active material is fixed to the inner circumference of the insulating ring 2. It consists of a solid electrolyte tube 4 made of polycrystalline β°°-alumina forming a downwardly extending cylindrical bag tube having the function of selectively transmitting sodium ions Na+.

Further, an elongated cathode tube 5 extending through the cathode container 3 to the bottom of the solid electrolyte tube 4 is supported through the center of the upper lid of the cathode container 3 .

During discharge, sodium ions pass through the solid electrolyte tube 4 and react with the sulfur S in the anode container 1 to produce sodium polysulfide through the following reaction.

2Na+XS→Na2Sx Also, during charging, a reaction opposite to that during discharging occurs, and sodium Na and sulfur S are generated.

The solid electrolyte tube 4 of the sodium-sulfur battery configured as described above is made of granules containing polycrystalline β-peralumina before being press-molded, so it is assembled into a rubber press-molding device (as shown in FIG. 4). A rigid inner mold 11 and a rubber outer mold 1 make up the isostatic press machine.
The so-called rubber press molding method is used in which the polycrystalline β''-alumina-containing powder is filled into the gap between the mold 12 and the mold 12, and the outer peripheral surface of the outer mold 12 is statically pressed at a predetermined pressure P by storing the powder in a high-pressure container. Then, pressure is applied uniformly to the entire solid electrolyte tube 4 so that the density of the product becomes uniform.

(Problems to be Solved by the Invention) The solid electrolyte tube 4 obtained by the rubber press molding method as described above has an inner mold 11 having a rigid inner surface 4b.
Since each powder 6 is densely compressed and the inner surface 4b becomes quite smooth as shown on the left side of FIG. 5, sodium ions permeate through the solid electrolyte tube 4 evenly during discharge. However, there is no problem because
Since the outer surface 4a of the solid electrolyte tube 4 is formed by a non-rigid rubber mold 12, its surface condition is not necessarily smooth and uniform, as shown on the right side of FIG. If roughness Ra is defined as the sum of all the heights h of each convex part 7 divided by the number of convex parts, then the average roughness Ra of this outer surface 4a is compared to the average roughness of the inner surface. and become very rough. Further, the maximum height Rma of the convex portion 7
x also becomes larger. As a result, when the solid electrolyte tube 4 is in use, as shown in FIG. Therefore, current is concentrated there, and the valley portion 8 is likely to deteriorate. Furthermore, when the sodium-sulfur battery is heated or cooled, thermal stress tends to concentrate in the valleys 8.

Therefore, there was a problem that cracks were more likely to occur in the valleys 8, the life of the solid electrolyte tube 4 was shortened, and the reliability of the battery was lowered.

A first object of the present invention is to provide a solid electrolyte tube for a sodium-sulfur battery that can improve durability and reliability.

A second object of the present invention is to provide a method for shaping the surface of a solid electrolyte tube, which allows easy surface shaping.

A third object of the present invention is to provide a method for shaping the surface of a solid electrolyte tube, which can further improve the surface roughness in addition to the second object.

Furthermore, a fourth object of the present invention is to provide a method for shaping the surface of a solid electrolyte tube, which can form the solid electrolyte tube to desired dimensions and further smooth the surface roughness. It is in.

(Means for Solving the Problems) In order to achieve the first object, the solid electrolyte tube according to claim 1 is characterized in that the number of convex portions is calculated by adding up the heights of the convex portions formed on the surface of the solid electrolyte tube. The average height divided by the average height of the surface is defined as the average roughness of the surface, the average roughness is 2.0 μm or less, and the maximum height of the convex portion is 15 μm or less.

A first method of surface shaping a solid electrolyte tube according to claim 2 includes:
In order to achieve the second objective, a method is adopted in which the outer surface of the solid electrolyte tube is shaped using a shaping device while the surface of the solid electrolyte tube is in an unfired and undegreased state.

A second method for shaping the surface of a solid electrolyte tube according to claim 2 includes:
In order to achieve the third objective, a method is adopted in which the outer surface of the solid electrolyte tube is shaped by a shaping device after the solid electrolyte tube has been degreased and calcined.

A third aspect of the solid electrolyte tube surface shaping method according to claim 2 is:
In order to achieve the fourth objective, a method is adopted in which the solid electrolyte tube is degreased and the outer surface of the solid electrolyte tube is shaped using a shaping device in the state of a fired body.

(Function) Since the solid electrolyte tube according to claim 1 has a fine surface roughness, when it is used in a sodium-sulfur battery, sodium ions, sulfur, and even sodium polysulfide that come into contact with the solid electrolyte tube surface are absorbed into the solid electrolyte. It is no longer concentrated locally on the tube surface, and the sodium-sulfur battery is heated.
When the solid electrolyte tube is cooled, the concentration of thermal stress on the surface of the solid electrolyte tube is alleviated, so deterioration of the solid electrolyte tube is suppressed.

Moreover, the first method of surface shaping of a solid electrolyte tube according to claim 2
Since the surface of the solid electrolyte tube of the unfired formed body is softer than that of the sintered body, there is a great advantage that it can be easily shaped.

A second method for shaping the surface of a solid electrolyte tube according to claim 2 includes:
Since the surface of the degreased and calcined solid electrolyte tube can be shaped in a state close to that of the unfired formed body, shaping is easy and the surface roughness after shaping becomes fine.

The third aspect of the method for manufacturing a solid electrolyte tube according to claim 2 is that the surface of the solid electrolyte tube after firing is shaped, so that the surface roughness can be made even finer to the same level as the polishing roughness, and the final desired state of the solid electrolyte tube can be achieved. It has the great advantage of being able to be formed to any size.

(First Example) Next, a first example that embodies the method of manufacturing a solid electrolyte tube for a sodium-sulfur battery according to the present invention will be described.

First, α-alumina, sodium carbonate, and lithium oxalate prepared in a predetermined proportion are pulverized and mixed by wet pulverization using, for example, a 1001 ball mill.

Thereafter, a powder having a predetermined particle size (average particle size of 40 to 120 μm) is preferably granulated using a spray dryer.

Next, a rubber press molding device (isostatic press machine) is used, and at a pressure of 2.5 tons/cd, for example, the outer diameter is 15 mm and the wall thickness is 1 mm. On, a solid electrolyte tube 4 (see FIG. 2) having a bag tube shape and having a length of 150 nm is formed.

Further, the surface 4a of the solid electrolyte tube 4 in the unfired and undegreased formed state is dry polished with a diamond grindstone (#180) using a centerless grinder.

Next, surface finishing is performed using a paper wiper or a nylon mesh to complete the shaping of the outer surface of the solid electrolyte tube.

Then, it was degreased at about 1000℃ for 2 hours, and then heated to about 1600℃ for 1 hour.
After firing for 0 minutes, a solid electrolyte tube made of β''-alumina and suitable for a sodium-sulfur battery was obtained.

The surface 4a of the solid electrolyte tube 4 manufactured in this manner was smooth as shown in FIG.

The average roughness Ra of the surface 4a is 0 as shown in the table.
．． 5~0.8μm 1 Also, the maximum height Rmax of the convex part is 6~
It was 11 μm.

Note that during the rubber press molding, the average surface roughness Ra of the inner circumferential surface of the solid electrolyte tube 4 is 0.5 μm or less, and the maximum height Rmax of the convex portion is 5.0 μm or less.
This is particularly desirable in order to facilitate the movement of the cathode active material from the inside of the solid electrolyte tube 4 to the outside.

(Second Example) In this second example, the unfired and undegreased solid electrolyte tube 4 produced in the first example described above was degreased at about 1000°C for 2 hours, and then the centerless Solid electrolyte tube 4 in a pre-fired state that has been degreased using a grinder
Dry process the surface with a diamond grindstone (#180).

Finally, the solid electrolyte tube 4 was obtained by firing at about 1610° C. for 5 minutes. The average surface roughness Ra of this solid electrolyte tube 4 is
As shown in the table, the surface average roughness Ra was 0.2 to 0.4 μm, which was even better than the surface average roughness Ra of the solid electrolyte tube obtained in the first example. In addition, the maximum height Rmax of the convex portion is 2 to 6 μm.
It was smoother than the solid electrolyte tube 4 of the first example.

(Third Example) In this third example, the solid electrolyte tube 4 in the unfired, undegreased state obtained in the first example was heated to about 1590°C.
After firing for 5 minutes, use a centerless grinder to grind the surface 4a of the solid electrolyte tube 4 in a sintered state with a diamond grindstone (9
800), and further wet processing was performed using a #1200 diamond grindstone.

The surface average roughness Ra of this solid electrolyte tube 4 was 0.2 to 0.4 μm as shown in the table, which was as good as the surface average roughness Ra of the solid electrolyte tube obtained in the second example. . or,
The maximum height Rmax of the convex portion was also 2 to 6 μm, similar to the solid electrolyte tube 4 of the second example.

Note that the present invention can also be embodied as follows.

In each of the above examples, a centerless grinder equipped with a diamond grinding wheel was used as the shaping device, but in this case, it is of course possible to change the average surface roughness by changing the number and particle size of the diamond grinding wheel. Also in each of the above embodiments, the average surface roughness can be made even finer by making the grain size of the diamond grinding wheel finer. Furthermore, the structure may be modified as desired within the scope of the claims of the present invention, such as using a lathe or cylindrical grinder instead of a centerless grinder, or using a processing method using abrasive grains. is also possible.

(Effect of the invention) Since the solid electrolyte tube according to claim 1 has a small average roughness on its surface, it improves the surface strength, and when the solid electrolyte tube is used in a sodium-sulfur battery, it is possible to prevent sodium ions from forming on the surface. Alternatively, it is effective in preventing local concentration of sulfur, sodium polysulfide, and thermal stress, thereby improving the durability of the solid electrolyte tube.

Further, the method for shaping the surface of a solid electrolyte tube according to claim 2 can easily shape the surface of a solid electrolyte tube that is an unfired product, and can also shape the surface of a solid electrolyte tube that has been degreased and calcined. Since the surface can be shaped in the same way as the shape, the average surface roughness after firing can be made finer.Furthermore, since the surface of the solid electrolyte tube of the sintered body is shaped after firing, the surface average roughness can be made finer. It is possible to obtain a solid electrolyte tube with high dimensional accuracy, in which the roughness can be made as fine as described above, and the dimensions of the solid electrolyte tube can be completely matched to the desired dimensions of the final product.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of part A in FIG. 2 of a solid electrolyte tube showing an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of the central part of the solid electrolyte tube, and FIG. 3 is a sodium Figure 4 is a vertical cross-sectional view of the central part of a sulfur battery, Figure 4 is a vertical cross-sectional view of the central part for explaining the method of forming solid electrolyte tubes, Figure 5 is an enlarged cross-sectional view of part B in Figure 4, and Figure 6 is a solid electrolyte tube. FIG. 3 is an enlarged partial cross-sectional view of the surface of an electrolyte tube. 4...Solid electrolyte tube, 4a...Outer surface, 4b...
- Inner surface, Ra: Average surface roughness of the solid electrolyte tube in the fired state, h: Height of the convex portion 7, Rmax: Maximum height of the surface of the solid electrolyte tube. Patent applicant Tokyo Electric Power Company Nippon Insulator Co., Ltd.
Co., Ltd.

Claims (1)

[Claims] 1. The average height obtained by summing the heights (h) of the convex portions (7) formed on the surface (4a) of the solid electrolyte tube (4) and dividing the sum by the number of convex portions as described above. Sodium characterized in that the average roughness (Ra) of the surface (4a) is 2.0 μm or less, and the maximum height (Rmax) of the convex portion (7) is 15 μm or less. - Solid electrolyte tubes for sulfur batteries. 2. The method for a sodium-sulfur battery according to claim 1, wherein the outer surface of the solid electrolyte tube of any one of the formed body after compression molding, the degreased calcined body, and the fired body is shaped by a shaping device. Surface shaping method for solid electrolyte tubes.